This invention relates to a molded article for use in circuit formation formed by using thermoplastic resin compositions as injection molding materials and molding these resins by two-shot injection molding.
A molded article for use in circuit formation formed by two-shot injection molding refers to a molded article formed by first forming a predetermined shape by the primary molding of a primary thermoplastic resin to give a molded article of the primary resin, subjecting the molded resin to etching and catalyst application as a pretreatment for plating, placing the pretreated article in a mold having a cavity which is in conformity with the entire shape of the molded article for use in circuit formation, filling the space with a secondary thermoplastic resin so as to leave the circuit formation portion of the primary molded article uncovered and integrally molding the secondary molding with the primary molding. The molded article thus formed is subjected to electroless plating to form a circuit on the uncovered area of the primary molded article, thus giving a final molded article having a circuit formed therein.
However, the adhesion between the molded article of the primary resin formed by the primary molding to that of the secondary resin formed by the secondary molding is usually so poor that problems arise when the plating solution penetrates through the interface between the primary and secondary molded articles during the electroless plating of the primary molded article after the two-shot molding so as to corrode the formed circuit or peeling occurs at the interface between the primary and secondary molded materials when the final product is used under severe conditions. These problems have been aided by improving the adhesion at the interface through improved resin flow obtained by elevating the cylinder temperature or the injection pressure of a molding machine during the secondary molding or by decreasing the differences in the mold shrinkage between the primary and secondary resins by preheating the molded primary resin to a temperature near the molding temperature of the secondary resin, setting it in the cavity, and performing the secondary molding.
However, these procedures have problems such as decreased mechanical strengths due to the degradation of the resin, breakage of the primary molded resin when subjected to the elevated injection pressure used in the secondary molding, and the deformation of the molded primary resin caused by the softening of the primary resin during heating. Even if the adhesion between the primary resin and the secondary resin is good and has no problem of air tightness just after being molded, there sometimes has been delamination caused by a heat hysteresis during a high-temperature/low-temperature cycle.